#include<stdio.h>
#include<math.h>
int main()
{
    double x1, y1, x2, y2, length;
    scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2);
    length = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
    printf("%.2f\n", length);
    return 0;
}